A Mass Spring Model for Hair Simulation

Abstract:
Our goal is to simulate the full hair geometry, consisting of ap-
proximately one hundred thousand hairs on a typical human head.
This will require scalable methods that can simulate every hair as
opposed to only a few guide hairs. Novel to this approach is that
the individual hair/hair interactions can be modeled with physical
parameters (friction, static attraction, etc.) at the scale of a single
hair as opposed to clumped or continuum interactions. In this vein,
we ﬁrst propose a new altitude spring model for preventing col-
lapse in the simulation of volumetric tetrahedra, and we show that
it is also applicable both to bending in cloth and torsion in hair.
We demonstrate that this new torsion model for hair behaves in
a fashion similar to more sophisticated models with signiﬁcantly
reduced computational cost. For added efﬁciency, we introduce
a semi-implicit discretization of standard springs that makes them
truly linear in multiple spatial dimensions and thus unconditionally
stable without requiring Newton-Raphson iteration. We also simu-
late complex hair/hair interactions including sticking and clumping
behavior, collisions with objects (e.g. head and shoulders) and self-
collisions. Notably, in line with our goal to simulate the full head
of hair, we do not generate any new hairs at render time.